Reactive silicone containing hydrogel formulations are used to make extended wear soft contact lens as silicone imparts high oxygen permeability, flexibility leading to comfort and reduced corneal complications. But these siloxane molecules lack inherent wettability and thereby a compromise is made between oxygen permeability and water uptake. Traditionally these siloxane monomers are blended with organic hydrophilic monomers to prepare curable monomer mixture which can be actinically or thermally cured. However, mixing siloxane and organic monomers lead to incompatibility causing macro-phase separation and development of opacity. A possible solution to this problem is to modify the siloxane monomers with organic moiety which restricts the phase separation to the micro-level increasing its compatibility in the curable mixture and brings in some inherent hydrophilicity. These organo-modified siloxane monomers are cured along with organic monomers in presence of cross-linkers.
Examples of prior attempts of such methodology include those described in U.S. Pat. Nos. 4,260,725; 5,352,714; 5,998,498; 6,867,245; 6,013,711; 6,207,782; 7,601,766; 7,557,231; 7,732,546; 7,781,558; 7,825,273. But this approach leads to a large number of unreacted monomers due to mismatch in the reactivity ratio of the monomers involved. Further, this method leads to uncontrolled cross-linking and molecular weight build-up, which affects the batch to batch reproducibility. Since there are multiple components involved in the formulation, the chances of having unreacted monomers are high and hence it is necessary to extract these leachable monomers from the matrix, such as by aqueous-organic solvent mixtures, which leads to increased processing costs.
U.S. Pat. No. 5,981,669 discloses the synthesis of a mono-functional pre-polymer by free radical polymerization of a silicone monomer and a hydrophilic monomer in the presence of a chain transfer agent. These pre-polymers were then introduced into formulations with bi-functional macromers, which may be composed of silicone. U.S. Patent Publication Nos. 2011/0166248 and 2008/0231798 discloses block copolymers of silicone containing monomers with hydrophilic monomers to yield a pre-polymer. U.S. Patent Publication No. 2010/0298446 and U.S. Pat. No. 8,642,712 report functionalization of polysiloxane blocks to act as a macro initiator for polymerizing a hydrophilic monomer via ATRP. This technique yields bi or tetra functional pre-polymers. U.S. Patent Publication No. 2010/0296049 and U.S. Pat. No. 8,557,940 discloses RAFT technique for polymerizing a mixture of bi-functional polysiloxane polymer and organic monomer. U.S. Patent Publication No. 2009/0143499 covers a pre-polymer made of polysiloxane blocks, poly(oxyalkylene) blocks, and cross-linkable groups. U.S. Patent Publication No. 2014/0235782 discloses pre-polymer based on homo-polymerization of hydrophilic monomers. U.S. Patent Publication No. 2013/0172600 discloses pre-polymer approach wherein the polysiloxane units are used as a cross-linker to prepare the polymer and functionalization of the same. U.S. Pat. No. 7,550,519 discloses the FRP method to produce colored hydrogel lenses from reactive polymers.